1. Field of the Invention
The present invention relates to a multi-layered adhesive sheet which is processed into parts having an optimum shape, assembled, and thermally cured to form a structure. More particularly, the present invention relates to a multi-layered adhesive sheet which exhibits sufficient bonding strength even if the thickness of the sheet is reduced in order to reduce the weight of the heat exchanger, and which can be bonded without lifting even when assembled into a curved shape, a material for forming a heat exchanger, and a heat exchanger.
2. Description of Background Art
In the case of manufacturing an aluminum heat exchanger, an aluminum sheet is processed into parts having a specific shape, and the resulting parts are assembled. As the aluminum sheet, an aluminum material with a thickness of about 500–1000 μm is used as a core material, and an aluminum material as a filler metal having a melting point lower than that of the aluminum material as the core material is stacked on one side or each side of the core material (see JP-A-2002-47523).
A filler metal made of aluminum generally has a melting temperature of about 577° C. and must be heated to a brazing temperature (about 600° C.) equal to or greater than the melting temperature during joining. This increases the amount of energy consumed during brazing. Therefore, an aluminum sheet coated with a resin instead of a filler metal made of aluminum has been proposed (JP-A-2002-243395).
In recent years, reduction of the weight of heat exchangers has been demanded for automotive air conditioner applications or the like. To deal with this demand, the thickness of the aluminum material used as the core material must be reduced to 100 μm or less. However, since the strength of the aluminum material is decreased by reducing the thickness of the aluminum material, it is necessary to use a high-strength aluminum alloy to which an element such as magnesium, copper, or silicon is added in order to increase the strength of the core material.
The strength of the alloy is increased by increasing the amount of element to be added. However, the brazability of the aluminum sheet on which a filler metal is stacked decreases to a large extent due to a decrease in the melting point or the like.
An aluminum sheet coated with a resin has been proposed in order to reduce energy consumption. However, this aluminum sheet exhibits insufficient bonding strength in a curved section or has inferior heat resistance. Therefore, an adhesive sheet material having sufficient reliability and replacing brazing has been demanded.